There have been more tornadoes this month than in any other month on record, CBS News correspondent Elaine Quijano reports. More than 600 have been reported so far throughout the United States. The average for April is 160. The old record for any month was 542, in May 2003.

In the wake of a powerful tornado that ripped through here Wednesday, David Nadler of the National Weather Service is documenting the devastation to determine just how large and forceful a storm it was.

"This type of damage you're looking at is wind speeds over 110, 120 miles per hour," Nadler said.

Nadler's team conducts what amounts to a forensic investigation, reconstructing the scene of the crime, but at the National Severe Storms Laboratory in Norman, Okla., they saw the lawlessness waiting to happen.

"About a week ago, there were hints that there was something potentially big happening in the middle of this week sometime," said meteorologist Harold Brooks, who works at the laboratory.

Brooks said a storm system coming in from the cold Rocky Mountains was on a collision course with a low pressure system bringing warm, moist air from the Gulf of Mexico -- perfect conditions for a perfect storm.

"The winds were strong out of the South at low levels and strong out of the West at higher levels and that meant storms became organized in such a way they were able to produce horrific tornadoes," Brooks said.

So what's triggering all these twisters? Some experts believe a lingering La Niña system in the Pacific has shifted the pattern of wind flows across the United States. Others blame an unusually strong jet stream.

Back in Alabama, Nadler believes there are other reasons storms in the South are so deadly.

"We can get a lot more tornadoes during the nighttime hours, and people's awareness to what's going on around them at night is certainly going to be lower than it is during the day, not to mention visibility is a lot worse," Brooks said.

Fortunately forecasters say the worst is over. There's no more bad weather expected in the region at least for the next week.

Elaine Quijano was named a CBS News correspondent in January 2010. Quijano reports for "CBS This Morning" and the "CBS Evening News," and contributes across all CBS News platforms. She is based in New York.